engine cut out at high speed...

scratch · December 19, 2005, 07:25:14 PM

It was a temporary starvation of fuel due to the lack of adequate vacuum to draw enough fuel to continue the combustion process. The bike cut out when he chopped the throttle, he 'starved' it.

Badger · December 19, 2005, 07:45:53 PM

Quote from: scratchIt was a temporary starvation of fuel due to the lack of adequate vacuum to draw enough fuel to continue the combustion process. The bike cut out when he chopped the throttle, he 'starved' it.

I'd think that might cause the engine to miss...but why wouldn't it restart as it slowed? In gear, engine stopped, throttle open, shouldn't it develop enough vacuum to pull fuel through? Did positive pressure develop in the system that would prevent sufficient vaccum to draw fuel/air?

Just so that I understand: the solution to this situation is to do nothing for an indeterminate period of time (but longer than it takes for the bike to roll to a stop), then make believe nothing happened. No need to prime the engine, no need to do anything other than press the starter after whatever it is works itself out.

Is it just me or does that sound...wrong?

scratch · December 19, 2005, 07:56:33 PM

Quote from: BadgerI'd think that might cause the engine to miss...but why wouldn't it restart as it slowed? In gear, engine stopped, throttle open, shouldn't it develop enough vacuum to pull fuel through? Did positive pressure develop in the system that would prevent sufficient vaccum to draw fuel/air?

Either it couldn't due to vacuum in the tank or the floatbowls were empty.

Quote from: BadgerJust so that I understand: the solution to this situation is to do nothing for an indeterminate period of time (but longer than it takes for the bike to roll to a stop), then make believe nothing happened. No need to prime the engine, no need to do anything other than press the starter after whatever it is works itself out.

Is it just me or does that sound...wrong?

You are correct. The first thing I would do is switch to Prime. If that doesn't work, then open the tank. Not all of us know to do this. And, when it happened to me, I totally forgot what I was supposed to do (brain fart).

Badger · December 19, 2005, 08:30:25 PM

Quote from: scratchEither it couldn't due to vacuum in the tank or the floatbowls were empty.

Vacuum in the tank == engine stops regardless of throttle position. I think it is unlikely a random coincidence that both sgaterboy and I both had similar experiences when coming off the throttle. Floatbowls empty == engine won't start without prime, right?

Quote from: scratchYou are correct. The first thing I would do is switch to Prime. If that doesn't work, then open the tank. Not all of us know to do this. And, when it happened to me, I totally forgot what I was supposed to do (brain fart).

When my engine cut out, I did neither. Now if it was vacuum in the tank, it would slowly equalize (and thus fix itself) through the normal vent..but that would still have emptied the floats, right? Would the floats fill without the petcock in prime? If not, this definitely wasn't my problem, because I didn't switch it to prime, but it started just fine anyway (after a few moments of utter confusion).

In my understanding of The Way Things Work (which is probably wrong), there seems to be something wrong with the fuel starvation explanation...several bits just don't seem to fit.

JamesG · December 20, 2005, 07:47:39 AM

The mysterious temporarily lazy GS phenomenon has been discussed many times here over the years. Do a search if you want to read about it at length.
Quite a few people have experianced it, I have had it happen to me several times. In every case its always a fuel supply problem. A problem with the carbs would manifest itself differently (it would run like crap at a specific rpm from the begining and wouldn't go away by itself).
There are two schools of thought on it, that its the tank vacumm locking and that its a failure of the engine vacumm operated petcock valve.

The GS is a great bike, but it was designed as a entry level commuter. It was designed to putter around town and run at 55 mph down the highway, and to be honest was built for that with the cheapest parts and materials that Suzuki could get away with. Exceding that "performance envelope" like running at WOT at 100+mhp for extended periods of time causes that short coming to become apparent.

Badger · December 20, 2005, 08:58:24 AM

Quote from: JamesGThe mysterious temporarily lazy GS phenomenon has been discussed many times here over the years. Do a search if you want to read about it at length.

I have searched and read the discussions. I even posted a link to what I thought was a rational explanation...which you dismissed as "that's not the way reciprocating engines work." There seem to be different sets symptoms that you are lumping together as "the carbs/petcock/fuel system are crap"

1.) Fuel starvation at high fuel consumption (weary petcock issue, insufficient fuel supply)
2.) Runs poorly at specific RPM (jetting issue?).
3.) Engine stops when throttle is closed after being run at high speed (perhaps tank vacuum lock?)

After reading through the myriad different (and often conflicting) opinions, I'm still confused about how closing the throttle would abruptly vacuum lock the fuel tank (since that seems to be the most plausible and accepted explanation) after it's been running quite happily at high fuel consumption for some time. I have not yet seen any explanation that correlates the problem with closing the throttle.

Not that it's important...the problem seems to pass without incident (at least, after you pull off to the side of the road), and the solution seems to be to not chop the throttle to idle from high speed.

I'm just curious because there seems to be agreement that the problem is something that I don't believe is possible given my understanding of The Way Things Work...thus I have to assume that my understanding is incorrect, since you folks obviously know a lot more about this than I do.

:dunno:

scratch · December 20, 2005, 09:34:47 AM

Quote from: BadgerAfter reading through the myriad different (and often conflicting) opinions, I'm still confused about how closing the throttle would abruptly vacuum lock the fuel tank (since that seems to be the most plausible and accepted explanation) after it's been running quite happily at high fuel consumption for some time. I have not yet seen any explanation that correlates the problem to closing the throttle.

It had been running fine at that consumption rate because the vacuum hadn't developed yet. It is possible the vacuum in the tank overcame the demand for fuel at that time.

Quote from: BadgerNot that it's important...the problem seems to pass without incident (at least, after you pull off to the side of the road), and the solution seems to be to not chop the throttle to idle from high speed.

Yes, don't do that!

Quote from: BadgerI'm just curious because there seems to be agreement that the problem is something that I don't believe is possible given my understanding of The Way Things Work...thus I have to assume that my understanding is incorrect, since you folks obviously know a lot more about this than I do.

We're here to help.

Badger · December 20, 2005, 10:28:11 AM

Quote from: scratch
Quote from: BadgerI have not yet seen any explanation that correlates the problem to closing the throttle.
It had been running fine at that consumption rate because the vacuum hadn't developed yet. It is possible the vacuum in the tank overcame the demand for fuel at that time.

Color me incredulous, but I am disinclined to believe that it was mere happenstance that a terminal vacuum developed at exactly the same time the throttle position changed dramatically (from open to idle). *shrug* I assume that going from open to idle (or subsequently back to open) was a main contributor to the issue, rather than a coincidence.

One more thing that's got me confused: with the engine stopped, in 6th gear, decelerating from 80mph, the tach needle was flat at 0. I noticed this while twisting the throttle to no avail, because I initially thought it might be a chain or transmission problem (i.e., engine running but not transferring power to the wheel). I would have assumed that even with the engine not combusting, it would still be driven by the wheel and therefore turning and thus should register on the tach. Is there an explanation for this, or am I missing something? (this led me to think it was an electrical failure, but the speedo and lights were still functional).

Badger · December 20, 2005, 10:29:14 AM

Quote from: scratchWe're here to help.

btw: I appreciate the insight.

Roadstergal · December 20, 2005, 10:54:14 AM

I agree with you that the given explanation for the phenomenon you are describing is not adequate. I have yet to experience it m'self...

However, I don't remember what bike you have, but isn't the tach on the current 500s ignition-driven? Would it then only work if the engine were running?

Badger · December 20, 2005, 10:57:51 AM

Quote from: RoadstergalHowever, I don't remember what bike you have, but isn't the tach on the current 500s ignition-driven? Would it then only work if the engine were running?

Didn't know that (but suspected as much). I have an '05, so that would certainly explain that away.

bubba zanetti · January 23, 2006, 03:19:17 AM

Thanks guys & gals for your knowledge.

I had the bike cut out on me this arternoon. I took the long way home which is mostly 100k/h speed limits. I get to a good stretch of road & decide to open it up.

Sitting on about 150k/h for a short stretch the bike gave a 'hiccup' and then lost power. I rolled to a stop and tried to restart the bike, with no luck.

Remembering this thread I let the bike sit a few minutes and then tried it again, bingo it started up.

BTW the temperature was fairly warm today, around mid to high 30c when I was riding.

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engine cut out at high speed...